This invention relates in general to low cost flyback type power supplies and in particular to a novel apparatus for providing a low voltage regulated flyback power supply at minimal cost.
Flyback type power supplies are well known in the art and extensively used because of their low cost and light weight. The drawback of a flyback supply is that it only delivers energy when the flyback switch is open which makes the task of controlling the output voltage more difficult. In many computer related circuits, the nominal 5 volt winding of the flyback transformer is heavily regulated whereas the nominal 12 volt winding may not be. In such instance, the output voltage across the filter capacitor in the 12 volt supply may rise to 13.3 volts or more under no load conditions. This is not desirable and is generally countered by adding a bleed resistor across the capacitor or by using a linear voltage regulator in the 12 volt supply line. The bleed resistor wastes power and generates heat and does not represent a desirable solution, especially in a compact, low cost power supply. The linear regulator is similarly neither a size or a cost effective solution.
With the present invention, a small saturable transformer is used to preclude the usual voltage rise at the output of the power supply under no load conditions and yet not inhibit full energy transfer under load conditions. While the invention is particularly useful in small flyback type power supplies, it may be advantageous used with other power supplies having similar topologies.